Process for the fibrous esterifica



Patented A t. 7,. 1936 PATENT OFFICE PROCESS FOR THE FIBROUS ESTERIFICA- TION F CELLULOSE EMPLOYING HOMO- GENIZERS OF THE BENZENE SERIES Edward C. Yackel and William 0. Kenyon, Rochester, N. Y., assignors to Eastman Kodak Company, Rochester, N. Y., a corporation of New York No Drawing. Application May- 19, 1933, Serial No. 671,899

7 Claims.

The present invention relates to a process of esterifying cellulose in a bath in which a saturated hydrocarbon is employed as the non-solvent and an aromatic hydrocarbon is present to assure homogeneity of the constituents of the bath.

Among the most effective non-solvents known for the fibrous esterification of cellulose are the saturated hydrocarbons either aliphatic such as hexane or heptane mixtures or alicyclic such as cyclohexane. Some of these non-solvents are known in the trade under the names of ligroin,

petroleum ether, Stoddard solvent, kerosene, gasoline, naphtha, etc. Stoddard solvent is a commonly known distillate which is described in Bureau of Standards Bulletin C. S. 3-28 (1929). Due to their effectiveness a less amount of this type of non-solvent is necessary to assure nonsolvency than is the case with the non-so1vents which are ordinarily employed. However these non-solvents suffer the disadvantage that their mixture with the, fatty acid anhydrides are heterogeneous especially in those cases where hydrocarbons having a high boiling range are employed. It is true that cellulose may be esterified in a heterogeneous bath consisting of fatty acid anhydride, non-solvent and a catalyst but the product resulting from such a product is degraded, usually being a powder and is not suitable for the preparation of sheeting or film. It was with a View of rendering a mixture of an aliphatic hydrocarbon non-solvent and a lower fatty acid anhydride suitable for preparing cellulose esters that Minsk, Kenyon and Gray discovered the homogenizing of this mixture which renders, it eminently suitable for esterifying cellulose which invention they have disclosed and claimed in their application Serial No. 671,900 filed of even date.

One object of our invention is to provide a process for the fibrous esterification of cellulose in which a saturated hydrocarbon is employed as the non-solvent and the bath is rendered homogeneous by employing an aromatic hydrocarbon as the homogenizing agent. Another object of our invention is to provide a process for the fibrous esterification of cellulose embodying all the advantages inherent in the use of a saturated hydrocarbon but in which all the reagents therein are compatible so that a uniform esterification of the cellulose is assured.

We have found that a fibrous esterification bath in which a saturated hydrocarbon is the non-solvent may be homogenized by the addition thereto of an aromatic hydrocarbon such as benzene, toluene, Xylene and cymene in a substantial amount.

In a fibrous esterification process in which a saturated hydrocarbon is employed as the nonsolvent, a surprisingly small proportion of that hydrocarbon is necessary to render the esterification bath non-solvent of the cellulose ester formed, however, the non-solvency of this liquid is so pronounced that it extends even to constituents of the esterification bath. By the present invention the effectiveness of the saturated hydrocarbon to induce non-solvency of the cellulose ester by the esterification bath may be utilized and an even esterification of the cellulose is assured.

The following table shows the amount of the particular homogenizer which is necessary to as sure homogeneity in the given esterification bath. Obviously in instances where a different ratio of anhydride to hydrocarbon non-solvent is used, the amount of homogenizer may diifer from that given, however that amount will be determined by the effectiveness of the homogenizer. For example, with the proportions of saturated hydrocarbon to acetic anhydride as given below, 6 parts of xylene would be required where only 5 parts of toluene (by volume) would be suficient to homogenize an esterification bath. The parts given in the table are all based on volume.

- Amount of homo- Saturated Acetic ana hydrocarbon hydride gggggg gigg ggg 20 5 parts benzene 10 5 parts toluene 20 10 6 parts xylene In some esterifioation processes acetic or propi onic acid might be present and in that case it is only necessary to add sufficient acid or other homogenizer to supplement the effect of the organic acid present if it is present in insufficient amount to assure homogeneity of the esterification bath.

The following examples illustrate the applica? tion of our invention to the preparation of organic acid esters of cellulose.

Example I lbs. of a petroleum hydrocarbon having a boiling range of 150-200 C., 125 lbs. of toluene and 1 lb. of concentrated sulfuric acid was added to the pretreated mass and the temperature was permitted to rise from 20 to C. over a period of 5 hours. The whole was then kept at 50 C. until a sample showed complete solubility in a mixture of 95 parts of methylene chloride and 5 parts of methyl alcohol by volume. This esterification required about 10 hours. The fibers were then centrifuged and washed with toluene. The toluene retained by the fibers was removed by boiling the fibers with water after which they were dried.

Example II 25 lbs. of cotton linters were pretreated with '75 lbs. of glacial acetic acid for 4 hours. The mass was then introduced into an esterifying bath composed of 100 lbs. of 95% acetic anhydride, 100 lbs. of 95% propionic anhydride, lbs. of toluene, 200 lbs. of a petroleum hydrocarbon having a boiling range of l50-230 C. and a small amount (about 1 lb.) of a catalyst composed of 3 parts of phosphoric acid and 1 part of sulfuric acid by volume. The esterification was carried out at 40 C. for approximately 20 hours after which the fiber was washed and dried as in the previous example. The ester formed was found to be exceptionally stable to heat without any stabilization treatment to which ordinary fibrous esters of cellulose must often be subjected.

Example III 23 C. The temperature was allowed to rise to 40 C. over a period of 2 hrs. and the whole was maintained at that temperature until the completion of the esterification which was a period of about 26 hours. The ester formed was separated from the reaction mixture in the usual manner and was found to be soluble in methylene chloride-ethyl alcohol (:10 by volume).

Example IV 25 lbs. of cotton linters were pretreated with 25 lbs. of glacial acetic acid at room temperature for 17 hours. A mixture of 195 lbs. of acetic anhydride, '73 lbs. of a petroleum distillate having a boiling range of -210 C. and '78 lbs. of benzene together with 2 lbs. of catalyst (3 volumes of phosphoric acid to 1 of sulfuric acid) was added to the pretreatment mass at a temperature of 23 C. The temperature was allowed to rise to 40 C. over a period of 2 hours. The mass was maintained at that temperature for about 26 hours or until the esterification was completed. The resulting ester was separated out in the usual manner and was found to be soluble in methylene chloride-alcohol (90: 10 by volume).

Our process is adapted to cellulose esterifica-,

tion processes generally for the preparation of organic acid esters of cellulose. Other esters than those of the specific examples which may be produced by our process are cellulose propionate,

I cellulose butyrate, cellulose acetate butyrate, cellulose propionate butyrate, etc. The present invention is especially adapted to the processes for preparing esters containing acyl groups of more carbon atoms than acetyl as many of the nonsolvents employed at the present time lessen in effectiveness as the proportion of those higher acyl groups increases.

Obviously the procedure in processes in accordance with our invention may be varied in accordance with the judgment of the individual operator. For instance the cellulose may be treated with the esterification bath for a time before the non-solvent is added, however, it is preferred that both the diluent and the esterifying ingredients be added together. Also the selection of the anhydride and catalyst to be employed and the proportions thereof will not vary the present process so as to place it outside the scope of the invention. As was pointed out previously each homogenizer exerts its own individual homogenizing effect in the esterification bath regardless of the presence of other homogenizers therein. Consequently a mixture of a plurality of homogenizers might be employed if desired which mixture would exert approximately the cumulative effect of the individual substances.

Various modifications of the present process may be made without departing from the scope of our invention. For instance if desired the nonsolvent may be added to the esterification bath after the acid anhydride has been mixed with the cellulose but before the cellulose has been esterified to a point at which it will lose its fibrous condition in the absence of the non-solvent.

We claim as our invention:

1. A process for preparing an organic acid ester of cellulose in fibrous form which comprises reacting upon the cellulose with an esterifying bath containing a lower fatty acid anhydride, a saturated hydrocarbon as the non-solvent and a lower hydrocarbon of the benzene series in sufiicient amount to assure compatibility of the ingredients of the bath, which bath will not dissolve the ester formed therein.

2. A process for preparing a cellulose acetate propionate in fibrous form which comprises esterifying cellulose with a bath containing propionic acid, acetic anhydride, a saturated hydrocarbon as the non-solvent and toluene in sufiicient amount to assure compatibility of the ingredients of the bath, which bath will not dissolve the ester formed therein.

3. A process for preparing an organic acid ester of cellulose in fibrous form which comprises reacting upon the cellulose with an esterifying bath contain ng a lower fatty acid anhydride, a

saturated hydrocarbon as the non-solvent and benzene in sufiicient amount to assure compatibility of the ingredients of the bath, which bath will not dissolve the ester formed therein.

4. A process for preparing an organic acid ester of cellulose in fibrous form which comprises reacting upon the cellulose with an esterifying bath containing a lower fatty acid anhydride, a

saturated hydrocarbon as the non-solvent and 6. A process for preparing a cellulose acetate p-ropionate in fibrous form which comprises esterifying cellulose with a bath containing propionic acid, acetic anhydride, a saturated hydrocarbon as the non-solvent and xylene in sufiicient amount to assure compatibility of the ingredients of the bath, which bath will not dissolve the ester formed therein.

7. A process for preparing a cellulose acetate 10 propionate in fibrous form which comprises esterifying cellulose with a bath containing propionic acid, acetic anhydride, a saturated hydrocarbon as the non-solvent and a lower hydrocarbon of the benzene series in suificient amount to assure compatibility of the ingredients of the bath, which bath will not dissolve the ester formed therein.

EDWARD C. YACKEL. WILLIAM O. KENYON. 

